Spring REST Client

• REST clients in Spring ( RestTemplate, RestClient, WebClient, and OpenFeign)
• used to consume or call external REST services.
• Aacting as HTTP clients for communicating with other APIs(send requests and receive responses).

Requirements for Consuming a REST API

When consuming an external REST service, you need to know:

• API URL – The endpoint of the target REST API.
• HTTP Method – e.g., GET, POST, PUT, or DELETE.
• Response Type – The Java type (class) expected in the response.
• Request Body – The data to send (if applicable).
• Required Headers – Such as Content-Type, Authorization, etc.

Handling JSON Responses

When the API returns a JSON payload, create a POJO class that matches the response structure. Pass this POJO class as the response type in RestTemplate.

Example:

[
    {
    "id": 1,
    "title": "Fjallraven - Foldsack No. 1 Backpack, Fits 15 Laptops",
    "price": 109.95,
    "description": "Your perfect pack for everyday use and walks in the forest."
    },
    .....
]

public class ProductDto {
    private int id;
    private String title;
    private double price;
    private String description;
}

ResponseEntity<ProductDto> response =
    restTemplate.getForEntity(url, ProductDto.class);

HttpEntity

HttpEntity is used to wrap both the request body and headers together.

HttpHeaders headers = new HttpHeaders();
headers.set("Authorization", "Bearer token");
headers.setContentType(MediaType.APPLICATION_JSON);

HttpEntity<ProductDtoRequest> entity = new HttpEntity<>(requestBody, headers);
ResponseEntity<ProductDto> response =  restTemplate.exchange(url, HttpMethod.POST, entity, ProductDto.class);

Comparison of REST API Clients in Spring Boot

Client Type	Synchronous	Asynchronous	Recommended For	Notes
RestTemplate	Yes	No	Simple apps	Deprecated but maintained
WebClient	No	Yes	Reactive systems	Best for scalable, non-blocking use cases
RestClient	Yes	Optional	Modern Spring Boot (3.2+)	Easiest and preferred API style today
OpenFeign	Yes	No	Microservices architecture	Declarative client with annotation support

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Github Code : Consuming REST API